Such linear compressors are, for example, known from U.S. Pat. Nos. 6,596,032 B2 or 6,642,377 B2.
During the operation of a compressor in a cooling device, situations may occur where the electrical power consumption of the compressor is unusually high and may lead to intense heating of the compressor. This may be the case, for example, when initially starting up the cooling device and/or after a lengthy stoppage time when the temperature of the entire interior of the cooling device has to be cooled down from a high initial temperature to a set operating temperature and the compressor has to be operated over a lengthy period of time without interruption, when, for example, due to a door not correctly closing, the flow of heat into the interior of the cooling device is increased, when the heat output from the condenser of the cooling device is hindered or when the movement of the compressor itself is disrupted by a mechanical defect. Such situations have to be reliably identified in order to limit the power consumption of the compressor, so that there is no fire risk as a result of overheating the compressor. In conventional cooling devices with a rotatably driven compressor, this object is generally achieved by means of a temperature sensor which is attached to the housing of the compressor, and a control circuit which, using the measured values supplied by the temperature sensor, makes a decision about a possible reduction in the electrical power supplied to the compressor.
A method for operating a linear compressor is known from KR 2002 021532-A in which a decision is made, using the electrical current intensity consumed by the compressor, as to whether the compressor is in an overload state or not, and the stroke of a piston of the compressor is reduced when an overload state is established.
As only the current consumption is used to decide whether an overload state is present or not, the limit value of the current consumption, above which an overload state is established, has to be sufficiently low that overheating is reliably avoided, even in possibly the most unfavorable operating conditions. The limit value has to be selected, therefore, such that overheating is eliminated even during long-lasting continuous operation of the compressor, such as when starting up the cooling device from a warm state. Operation at higher current intensities, which could be permitted without reservation during intermittent operation, when only a low temperature has to be maintained inside the cooling device, is thereby eliminated. The efficiency of the linear compressor is, therefore, not able to be fully utilized.